Raising Silkworms: Care, Mulberry Chow, and Storage

Silkworms (Bombyx mori) are unusual feeders. They eat nothing but mulberry, can't survive without human husbandry, and pupate on a strict 28-day schedule from hatch to cocoon. None of that makes them hard to keep, but they're unforgiving when the basics slip. Get a few specific things right and a batch reliably produces strong feeders for two to four weeks. Get them wrong and silkworms die fast.

What silkworms eat, and why

In the wild silkworms eat fresh mulberry leaves (Morus alba, white mulberry, mostly). Five thousand years of selective breeding made them obligate mulberry specialists, so they can't survive on any other plant. Since most keepers don't have a mulberry tree on hand, the standard food is mulberry chow.

What mulberry chow actually is

Commercial chow is dried, powdered mulberry leaf, usually with agar or carrageenan as a binder, sold as a dry mix. You combine it with hot water (typically 1:3 to 1:4 by volume per the package), let it set 5-10 minutes, and offer it as small chunks or a thin spread. Cooled chow holds shape so silkworms can climb on without sinking.

Fresh mulberry leaves as an alternative

If you have a mulberry tree (white, red, or black all work), fresh leaves can replace chow entirely. Wash, pat dry, and offer in handfuls. Silkworms grow faster on fresh leaves, but the leaves must be pesticide-free and fresh; wilted or contaminated leaves kill silkworms quickly.

Daily care

Temperature

72-82°F (22-28°C). Below 70°F they grow slowly; below 60°F they die. Above 85°F they grow faster but stress easily. Never refrigerate silkworms — cold is the single most common cause of mass die-offs. A draft-free spot at room temperature, a warm closet or shelf, is correct.

Container and ventilation

The shipping container is fine for the first batch. For larger or longer-term keeping, a shallow plastic bin (10-14 in across, 2-3 in deep) with a vented lid works well. Silkworms don't climb well, so deep walls aren't necessary.

Cleaning

Frass (small dark pellets) accumulates fast. Spot-clean every other day by shifting the silkworms onto fresh chow and discarding the old chow with the frass. They migrate to fresh food on their own, so a full bin teardown usually isn't needed.

Chow refresh schedule

Replace chow every 2-3 days. Old chow dries, molds, or gets too fouled with frass to be safe. Mold is a silkworm killer; once it appears, clean and reset the whole bin.

The 28-day silkworm lifecycle

Knowing where a batch sits helps you plan feedings:

• ◆Day 0-3: hatchlings, ~3 mm, eat constantly
• ◆Day 4-10: first/second instar, ~5-15 mm
• ◆Day 11-18: third/fourth instar, 15-35 mm, best feeding-size range
• ◆Day 19-25: fifth instar, 35-70 mm, good for adult beardies and panther chameleons
• ◆Day 26-28: pre-pupation, they stop eating, turn translucent, and spin

They grow especially fast in the third and fourth instars. A small silkworm on Tuesday can be a medium by Friday, so re-check sizing every few days.

Storing silkworms long-term

You can't pause silkworms. Once hatched they're on the clock and you either feed them off or let them pupate. Two strategies for smaller collections:

• ◆Order smaller, more frequent batches matched to your feed-off rate. A 50-count of small silkworms feeds one beardie comfortably for 2-3 weeks.
• ◆Stagger orders by 10-14 days so fresh small silkworms arrive before the previous batch outgrows usable size.

You cannot freeze or refrigerate to stall development. The lifecycle is the lifecycle.

Common keeper mistakes

• ◆Refrigerating to "make them last" — kills them
• ◆Feeding non-mulberry plants — they can't eat anything else
• ◆Letting chow dry out — cover with a damp paper towel between feedings if your air is dry
• ◆Mold — it kills in hours; spot-clean aggressively at the first fuzz or musty smell
• ◆Overcrowding — keep below ~30 silkworms per 10 sq in of floor
• ◆Pesticide-contaminated leaves — only use leaves from a tree you control

Letting silkworms pupate (optional)

If you want to breed or just watch the lifecycle: at day 25-28 they stop eating and search for a place to spin, so give them a clean dry area (paper towel works). Cocoons take about 3 days; don't disturb them. Adult moths emerge 12-16 days later, flightless and short-lived, just long enough to mate. Females lay 200-500 eggs, which need cold storage (~50°F) to enter diapause if you want to delay hatching. For most keepers it's not worth the effort versus simply ordering fresh batches, but it's a great learning project.

Bottom line

Silkworms aren't difficult, just unforgiving when care slips. Room temperature, fresh chow every 2-3 days, no mold, and a quick size check every few days. Do that and a batch reliably feeds your collection for weeks. Browse silkworms at All Angles Creatures to get started.

Related: Silkworms 101 and silkworms for chameleons.